Alphabet's Waymo self-driving cars that have been tested in the streets of California seems to be safer compared to last year, according to a report released today by the CA Department of Motor Vehicles (DMV.)

California requires auto companies and suppliers who test their self-driving vehicles on public roads to provide an annual compilation of miles traveled in autonomous mode and the number of "disengagements," or times the self-driving system was deactivated and control handed back to humans because of a system failure or a traffic, weather or road situation that required human intervention.

This year's California disengagement report shows a marked improvement in Google's fully self-driving technology.

Since 2015, Google's rate of safety-related disengages has fallen from 0.8 disengages per thousand miles to 0.2 per thousand miles in 2016. (Even as Google increased its driving by 50% in the state - racking up a total of 635,868 miles - the total number of reportable disengages fell from 341 in 2015 to 124 for this reporting period).

Waymo said that this four-fold improvement reflects the work the company has been doing to make its software and hardware "more capable and mature."

The company says it has made improvements to its technology because we use each of these disengages to teach and refine a car. For each event Waymo can create hundreds of related scenarios in simulation, varying the parameters such as the position and speed of other road users in the area. This allows the company to better identify the root cause of any disengage and resolve any problems.

Waymo said its fleet of self-driving vehicles logged more than 600,000 miles last year on public roads in California, while rival Tesla reported operating autonomous vehicles for just 550 miles on public roads since last October, according to reports released by the CA DMV.

Tesla Chief Executive Elon Musk has said the company plans to install new hardware and software to enable fully autonomous driving in Tesla vehicles before the end of the year. Tesla's four self-driving test vehicles compiled 550 miles, with a disengagement every 3.5 miles.

General Motors Co and its Cruise Automation affiliate logged nearly 10,000 miles in self-driving vehicles on California roads.

Nissan Motor Co tested a fleet that included three Leafs and two Infiniti Q50 sedans, logging 4,000 miles with a disengagement every 150 miles.

Ford Motor Co and Daimler AG's Mercedes-Benz said their self-driving vehicles logged fewer than 1,000 miles each last year in California, while Honda Motor Co and Volkswagen AG said they did not test self-driving vehicles on public roads in the state.